Google ReCaptcha not working on contact form

title: Contact
cache_enabled: false
form:
    name: contact-form
    action: '/contact#contact'
    fields:
        name:
            label: Name
            placeholder: Name
            type: text
            autofocus: true
            validate:
                required: true
        email:
            label: Email
            placeholder: Email
            type: text
            validate:
                required: true
        subject:
            label: Subject
            placeholder: Subject
            type: text
            validate:
                required: true
        message:
            label: Message
            placeholder: 'What''s on your mind?'
            type: textarea
            rows: 5
            validate:
                required: true
    buttons:
        submit:
            type: submit
            value: Send
    process:
        captcha: true
        reset: true
        email:
            from: '{{ config.plugins.email.from }}'
            to: '{{ config.plugins.email.to }}'
            subject: 'langford-assoc.com: {{ form.value.name|e }} - {{ form.value.subject|e }}'
            body: '{% include ''forms/data.html.twig'' %}'
        save:
            fileprefix: contact-
            dateformat: Ymd-His-u
            extension: txt
            body: '{% include ''forms/data.txt.twig'' %}'
        message: 'Thank you for getting in touch!'

captcha:
            recaptcha_secret: 6Le...ldK

        name: nome
        label: Nome
        placeholder: '(il tuo nome)'
        autofocus: 'on'
        autocomplete: 'on'
        type: text
        validate:
            required: true
    -
        name: email
        label: Email
        placeholder: '(la tua email)'
        type: text
        validate:
            rule: email
            required: true       
    -
        name: messaggio
        label: Messaggio
        size: long
        placeholder: "(inserisci il link e descrivi brevemente l'evento)"
        type: textarea
        validate:
            required: true        

g-recaptcha-response:
        label: Captcha
        type: captcha
        recaptcha_not_validated: 'Captcha not valid!'
buttons:
    submit:
        type: submit
        value: Invio
    reset:
        type: reset
        value: Reset
process:
    captcha: true
    email:
            from: '{{ config.plugins.email.from }}'
            to:
                - '{{ config.plugins.email.from }}'
                - '{{ form.value.email }}'
            subject: 'napoli360.it] un nuovo Evento da {{ form.value.email|e }}'
            body: '{% include ''forms/data.html.twig'' %}'
    save:
            fileprefix: feedback-
            dateformat: Ymd-His-u
            extension: txt
            body: '{% include ''forms/data.txt.twig'' %}'
    message: "Grazie per averci contattato ! tieni d'occhio Eventi Culturali Napoli"
    display: thankyou